To meet the demand for higher integration density and operating speed of LSIs, the effort to reduce the pattern rule is in rapid progress. At the present, the manufacture of 10 nm node logic devices and the manufacture of DRAM devices of 20 nm or less are approaching to a mass level. They are manufactured by a double patterning version of the ArF lithography. A study is also made on the lithography using EUV of wavelength 13.5 nm.
The flash memory, after pulling the miniaturization technology down to 15 nm, now shifts to a three-dimensional memory intended to increase the capacity by stereoscopic stacking. In this case, a technique for processing a ultra-thick film in excess of 10 nm is needed to process a multi-stage film laminate.
As the number of masks increases in the ArF double patterning lithography, it becomes necessary to improve the accuracy of alignment between plural masks and the accuracy of pattern size. Also for masks used in the EUV lithography, it is necessary to form a pattern of significantly finer size than the feature size in the ArF lithography and of higher accuracy.
The process for the manufacture of mask patterns involves formation of a resist pattern by EB writing. To increase the throughput of EB writing, a chemically amplified resist composition is generally used. The chemically amplified resist composition used herein is typically defined as comprising a polymer in the form of polyhydroxystyrene in which some hydroxyl groups are substituted with acid labile groups as a base resin, an acid generator, a quencher for controlling acid diffusion, a surfactant and an organic solvent. Despite the benefit of high sensitivity, this chemically amplified resist composition has the drawback that resolution and pattern accuracy are reduced by image blur due to acid diffusion.
As the resolution of resist pattern by EB writing improves, the aspect ratio of resist pattern increases, which raises the problem that pattern collapse occurs by the stresses applied during rinsing and drying after development. To prevent such inconvenience, a transition of resist film to a thinner film is proceeding. An improvement in dry etching resistance is necessary as well as the film thickness reduction. For improving the dry etching resistance of a resist film, positive resist compositions based on copolymers of acid labile group-substituted hydroxystyrene with indene and acenaphthylene are proposed in Patent Documents 1 and 2. By copolymerization of indene or acenaphthylene, not only dry etching resistance is improved, but also resolution is improved since acid diffusion is advantageously controlled.
As to the negative resist, negative resist compositions comprising a crosslinker or a base polymer containing crosslinking units are well known, whereas Patent Document 4 discloses a negative resist composition adapted to reduce hydrophilicity by acid-catalyzed dehydration reaction, comprising a polymer comprising recurring units derived from indene or acenaphthylene.
Nowadays, oxide film-bearing hard masks are applied as the mask substrate, eliminating a need for the extreme improvement in dry etching resistance of resist film. A better resolution is required for the resist film rather than the dry etching resistance improvement. Along with the resolution improvement, a reduction of edge roughness (LER, LWR) also becomes important at present.